The present application relates to an optical element and an imaging device. More specifically, the present application relates to an optical element utilizing an electrowetting phenomenon and an imaging device including the same.
In imaging optical systems used in imaging devices such as a still camera and a video camera, it is necessary for such imaging optical systems to have functions of adjusting the focus and adjusting the amount of light, to realize natural defocusing, to make the distribution of the amount of light on an image surface to be uniform etc. Among these requirements, in general, the requirement for adjusting the amount of light is met by a mechanical aperture mechanism including a plurality of movable blades.
However, such a mechanical aperture mechanism has the following problems: A mechanical driving unit for driving the movable blades is necessary, and thus the size of the device increases. In addition, in a small aperture state in which an opening of the aperture mechanism is small, diffraction of a light beam occurs, thereby decreasing the resolution of an acquired image. Furthermore, a sound is generated during the operation of the aperture mechanism.
To solve the above problems in such a mechanical aperture mechanism, optical elements using an electrocapillarity (electrowetting phenomenon) have been proposed (refer to, for example, Japanese Unexamined Patent Application Publication No. 2000-356792 (document '792)). FIG. 18 is a schematic view of an optical element disclosed in document '792. An optical element 100 described in document '792 is an optical element configured to control the amount of light beam 30 passing through the element (the amount of transmitted light).
The optical element 100 is configured so that a transparent substrate 102 and a transparent cover plate 106 are liquid-tightly sealed on a lower opening and an upper opening, respectively, of a cylindrical container 105 by adhesion or the like. A transparent electrode 103, an insulating layer 104, and a water-repellent film 111 are provided on the inner surface of the transparent substrate 102 in that order. A hydrophilic film 113 is provided on the inner surface of the transparent cover plate 106. A rod-shaped electrode 125 is provided so as to penetrate through the container 105, and an end of the rod-shaped electrode 125 is in contact with a first liquid 121. The first liquid 121 and a second liquid 122 are hermetically sealed in a space constituted by the hydrophilic film 113, the water-repellent film 111, and the inner wall of the container 105. The first liquid 121 is a liquid having electrical conductivity or polarity, and the second liquid 122 is a liquid that is immiscible with the first liquid 121. The refractive index of the first liquid 121 is substantially the same as the refractive index of the second liquid 122, but the transmittance of the first liquid 121 is different from the transmittance of the second liquid 122.
According to the optical element 100 described in document '792, a voltage is applied between the transparent electrode 103 and the rod-shaped electrode 125, and thus the shape of the interface between the two liquids is changed through the electrowetting phenomenon. As a result, a part of the surface of the second liquid 122 on the hydrophilic film 113 side contacts the hydrophilic film 113 to form on the hydrophilic film 113 an opening through which light can be transmitted (to form an optical path in the optical element 100). In this optical element 100, the size of the opening formed on the hydrophilic film 113 is changed by changing the voltage applied, thus adjusting the amount of light beam 30 passing through the optical element 100. That is, according to this optical element 100, the amount of light can be electrically controlled, and thus it is possible to solve the shortcomings of the mechanical aperture mechanism described above.